DOWNSTREAM HYDRAULIC GEOMETRY RELATIONSHIPS AMONG GEOMORPHIC PROCESS DOMAINS ALONG RIVER NETWORKS IN THE COLORADO FRONT RANGE

Many of the conceptual models developed for river networks emphasize progressive downstream trends in morphology and processes. Such models are well-suited for larger, low-gradient rivers, but can fall short in describing the extreme variability associated with headwater streams. Headwater streams occupy the majority of length of stream networks, provide unique biological productivity and habitat, and are sites of great sediment production. A more thorough understanding of the influence of local variability on process and form of headwater stream channels is required in order to predict channel geometry characteristics for management purposes. We defined local process domains based on glacial versus non-glacial valleys and levels of valley confinement. We then characterized 111 stream reaches in the Colorado Front Range with respect to process domain, stream type, and selected stream geometry characteristics. We tested the study reaches for significant differences in channel geometry and downstream hydraulic geometry relationships among stream types and process domains. Although downstream hydraulic geometry relationships are well-defined using all reaches in the study area, reaches in glacial valleys display much more variability than reaches in fluvial valleys, as evidenced in larger ranges of values for channel geometry variables and lower correlation values for downstream hydraulic geometry regressions. Streams flowing through inherited terrain in glacial valleys continue to adjust to sediment and water dynamics, and level of confinement influences locations of certain stream types. Thus, local variability associated with process domains overrides progressive downstream relationships in mountain headwaters, and field calibration of relations between reach-scale channel gradient and channel characteristics is necessary to predict process and form of headwater streams in the Colorado Front Range.